Mixed mode pulsing etching in plasma processing systems

ABSTRACT

A method for processing substrate in a chamber, which has at least one plasma generating source, a reactive gas source for providing reactive gas into the interior region of the chamber, and a non-reactive gas source for providing non-reactive gas into the interior region, is provided. The method includes performing a mixed-mode pulsing (MMP) preparation phase, including flowing reactive gas into the interior region and forming a first plasma to process the substrate that is disposed on a work piece holder. The method further includes performing a MMP reactive phase, including flowing at least non-reactive gas into the interior region, and forming a second plasma to process the substrate, the second plasma is formed with a reactive gas flow during the MMP reactive phase that is less than a reactive gas flow during the MMP preparation phase. Perform the method steps a plurality of times.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35 USC§120 to co-pending U.S. patent application Ser. No. 13/550,548 filed onJul. 16, 2012, entitled “Mixed Mode Pulsing Etching In Plasma ProcessingSystems,” which claims priority under 35 USC. 119(e) to a commonly-ownedU.S. Provisional Patent Application No. 61/581,054, filed on Dec. 28,2011, entitled “Mixed Mode Pulsing Etching In Plasma ProcessingSystems,” all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Plasma processing systems have long been employed to process substrates(e.g., wafers or flat panels or LCD panels) to form integrated circuitsor other electronic products. Popular plasma processing systems mayinclude capacitively coupled plasma processing systems (CCP) orinductively coupled plasma processing systems (ICP), among others.

Generally speaking, plasma substrate processing involves a balance ofions and radicals (also referred to as neutrals). As electronic devicesbecome smaller and/or more complex, etching requirements such asselectivity, uniformity, high aspect ratio, aspect dependent etching,etc., have increased. While it has been possible to perform etches onthe current generation of products by changing certain parameters suchas pressure, RF bias, power, etc., the next generation of smaller and/ormore sophisticated products demand different etch capabilities. The factthat ions and radicals cannot be more effectively decoupled andindependently controlled in the current art has limited and in somecases made it impractical to perform some etch processes to manufacturethese smaller and/or more sophisticated electronic devices in someplasma processing systems.

In the prior art, attempts have been made to obtain plasma conditions tomodulate the ion-to-radical ratio at different times during an etch. Ina conventional scheme, the source RF signal may be pulsed (e.g., on andoff) in order to obtain a plasma that has the normal ion to neutral fluxratio during one phase of the pulse cycle (e.g., the pulse on phase) anda plasma with lower ion to neutral flux ratio during another phase ofthe pulse cycle (e.g., during the pulse off phase). It is known thatsource RF signal may be pulsed synchronously with bias RF signal.

However, it has been observed that while the prior art pulsing has, tosome extent, resulted in alternate phases of normal ion to neutral fluxratio plasmas at different points in time and has opened up theoperating window for some processes, larger operating windows are stilldesired.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 shows, in accordance with one or more embodiments of theinvention, an example combination pulsing scheme where the input gas(such as reactant gas and/or inert gas) and the source RF signal areboth pulsed, albeit at different pulsing frequencies.

FIG. 2 shows, in accordance with one or more embodiments of theinvention, another example combination pulsing scheme.

FIG. 3 shows, in accordance with one or more embodiments of theinvention, yet another example combination pulsing scheme.

FIG. 4 shows, in accordance with one or more embodiments of theinvention, other possible combinations for the combination pulsingscheme.

FIG. 5 shows, in accordance with one or more embodiments of theinvention, the steps for performing combination pulsing.

FIG. 6 shows, in accordance with one or more embodiments of theinvention, the steps for performing gas pulsing.

FIGS. 7A and 7B illustrate, in accordance with embodiments of theinvention, different example variations of the gas pulsing schemediscussed in connection with FIG. 6.

FIG. 8 shows, in accordance with an embodiment of the invention,conceptual MMP etching cycles for the silicon etching example, with eachcycle involving at least an MMP preparation phase and an MMP reactivephase.

FIG. 9 shows, in accordance with an embodiment of the invention, otherconceptual MMP etching cycles where some ions exist in the MMPpreparation phase.

FIG. 10 shows, in accordance with an embodiment of the invention, amethod for performing MMP etching in a production ICP chamber.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described in detail with reference toa few embodiments thereof as illustrated in the accompanying drawings.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

Various embodiments are described hereinbelow, including methods andtechniques. It should be kept in mind that the invention might alsocover articles of manufacture that includes a computer readable mediumon which computer-readable instructions for carrying out embodiments ofthe inventive technique are stored. The computer readable medium mayinclude, for example, semiconductor, magnetic, opto-magnetic, optical,or other forms of computer readable medium for storing computer readablecode. Further, the invention may also cover apparatuses for practicingembodiments of the invention. Such apparatus may include circuits,dedicated and/or programmable, to carry out tasks pertaining toembodiments of the invention. Examples of such apparatus include ageneral-purpose computer and/or a dedicated computing device whenappropriately programmed and may include a combination of acomputer/computing device and dedicated/programmable circuits adaptedfor the various tasks pertaining to embodiments of the invention.

Embodiments of the invention related to a combination pulsing schemethat pulses the input gas (e.g., reactant gases and/or inert gases)using a first pulsing frequency and the source RF signal at a differentsecond pulsing frequency. Although an inductively coupled plasmaprocessing system and an inductive RF power source are employed todiscuss in the examples herein, it should be understood that embodimentsof the invention apply equally to capacitively coupled plasma processingsystems and capacitive RF power sources.

In one or more embodiments, the input gas is pulsed at a slower pulsingfrequency, and the inductive source RF signal is pulsed at a different,faster pulsing frequency in an inductively coupled plasma processingsystem. For example, if the inductive source RF signal is at 13.56 MHz,the inductive source RF signal may be pulsed at, for example, 100 Hzwhile the gas is pulsed at a different pulsing rate, such as 1 Hz.

Thus, a complete gas pulse cycle is 1 second in this example. If the gaspulsing duty cycle is 70%, the gas may be on for 70% of the 1-second gaspulsing period and off for 30% of the 1-second gas pulsing period. Sincethe source RF signal pulsing rate is 100 Hz, a complete RF signalpulsing period is 10 ms. If the RF pulsing duty cycle is 40%, the RFon-phase (when the 13.56 MHz signal is on) is 40% of the 10 ms RFpulsing period and the RF off phase (when the 13.56 MHz signal is off)is 60% of the 10 ms RF pulsing period.

In one or more embodiments, the inductive source RF signal may be pulsedwith two different frequencies while the gas is pulsed at its own gaspulsing frequency. For example, the aforementioned 13.56 MHz RF signalmay be pulsed not only at frequency f1 of 100 Hz but may also be pulsedwith a different, higher frequency during the on-phase of frequency f1.For example, if the RF pulsing duty cycle is 40% of the f1 pulse, theon-phase of f1 is 40% of 10 ms or 4 ms. However, during that 4 mson-phase of f1, the RF signal may also be pulsed at a different, higherfrequency of f2 (such as at 400 Hz).

Embodiments of the invention contemplate that the gas pulses and RFpulses may be synchronous (i.e., with matching leading edge and/orlowering edge of the pulse signals) or may be asynchronous. The dutycycle may be constant or may vary in a manner that is independent of theother pulsing frequency or in a manner that is dependent on the otherpulsing frequency.

In one or more embodiments, frequency chirping may be employed. Forexample, the RF signal may change its fundamental frequency in aperiodic or non-periodic manner so that during a phase or a portion of aphase of any of the pulsing periods (e.g., any of the RF signal or gaspulsing periods), a different frequency (e.g., 60 MHz versus 13.56 MHz)may be employed. Likewise, the gas pulsing frequency may be changed withtime in a periodic or non-periodic manner if desired.

In one or more embodiments, the aforementioned gas and source RF pulsingmay be combined with one or more pulsing or variation of anotherparameter (such as pulsing of the bias RF signal, pulsing of the DC biasto the electrode, pulsing of the multiple RF frequencies at differentpulsing frequencies, changing the phase of any of the parameters, etc.)

The features and advantages of embodiments of the invention may bebetter understood with reference to the figures and discussions thatfollow.

FIG. 1 shows, in accordance with an embodiment of the invention, anexample combination pulsing scheme where the input gas (such as reactantgas and/or inert gas) and the source RF signal are both pulsed, albeitat different pulsing frequencies. In the example of FIG. 1, the inputgas 102 is pulsed at a gas pulsing rate (defined as 1/T_(gp), whereT_(gp) is the period of the gas pulse) of about 2 seconds/pulse or 2MHz.

The TCP source RF signal 104 of 13.56 MHz is pulsed at a RF pulsing rate(defined as 1/T_(rfp), where T_(rfp) is the period of the RF pulsing).To clarify the concept of RF pulsing herein, the RF signal is on (suchas the 13.56 MHz RF signal) during the time period 120 and the RF signalis off during the time period 122. Each of the gas pulsing rate and theRF pulsing rate may have its own duty cycle (defined as the pulseon-time divided by the total pulsing period). There are no requirementsthat the duty cycle has to be 50% for any of the pulse signals, and theduty cycle may vary as needed for a particular process.

In an embodiment, the gas pulsing and the RF signal pulsing are at thesame duty cycle. In another embodiment, the gas pulsing and the RFsignal pulsing are at independently controllable (and may be different)duty cycles to maximize granular control. In one or more embodiments,the leading and/or trailing edges of the gas pulsing signal and the RFpulsing signal may be synchronous. In one or more embodiments, theleading and/or trailing edges of the gas pulsing signal and the RFpulsing signal may be asynchronous.

In FIG. 2, the gas input 202 is pulsed at its own gas pulsing frequency.However, the source RF signal 204 may be pulsed with two differentfrequencies while the gas is pulsed at its own gas pulsing frequency(defined as 1/T_(gp), where T_(gp) is the period of the gas pulse). Forexample, the RF signal may be pulsed not only at frequency f1 (definedas 1/T_(f1) from the figure) but may also be pulsed with a different,higher frequency during the on-phase of f1 pulsing. For example, duringthis on-phase of f1 pulsing, the RF signal may be pulsed at a differentpulsing frequency f2 (defined as 1/T_(f2) from the figure).

In FIG. 3, the gas input 302 is pulsed at its own gas pulsing frequency.However, the source RF signal 304 may be pulsed with three differentfrequencies while the gas is pulsed at its own gas pulsing frequency.For example, the RF signal may be pulsed not only at frequency f1(defined as 1/T_(f1) from the figure) but may also be pulsed with adifferent, higher frequency during the on-phase of f1 pulsing. Thus,during this on-phase of f1 pulsing, the RF signal may be pulsed at adifferent pulsing frequency f2 (defined as 1/T_(f2) from the figure.During the off-phase of f1 pulsing, the RF signal may be pulsed at adifferent pulsing frequency f3 (defined as 1/T_(f3) from the figure).

Additionally or alternatively, although the duty cycle is shown to beconstant in the examples of FIGS. 1-3, the duty cycle may also vary, ina periodic or non-periodic manner and independently or dependently onthe phases of one of the pulsing signals (whether gas pulsing signal, RFpulsing signal, or otherwise). Further, the change in the duty cycle maybe synchronous or asynchronous with respect to phase of any one of thepulsing signals (whether gas pulsing signal, RF pulsing signal, orotherwise).

In one embodiment, the duty cycle of the RF pulsing is advantageouslyset to be one value during the on-phase of the gas pulse (e.g., 154 inFIG. 1), and the duty cycle of the RF pulsing is set to be anotherdifferent value during the off-phase of the gas pulse (e.g., 156 of FIG.1). In a preferred embodiment, the duty cycle of the RF pulsing isadvantageously set to be one value during the on-phase of the gas pulse(e.g., 154 in FIG. 1) and the duty cycle of the RF pulsing is set to bea lower value during the off-phase of the gas pulse (e.g., 156 of FIG.1). It is contemplated that this RF pulsing duty cycle embodimentwherein the duty cycle is higher during the on phase of the gas pulsingand lower during the off phase of the gas pulsing is advantageous forsome etches. It is contemplated that this RF pulsing duty cycle variancewherein the duty cycle is lower during the on phase of the gas pulsingand higher during the off phase of the gas pulsing is advantageous forsome etches. As the term is employed herein, when a signal is pulsed,the duty cycle is other than 100% during the time when the signal ispulsed (i.e., pulsing and “always on” are two different concepts).

Additionally or alternatively, frequency chirping may be employed withany of the pulsing signals (whether gas pulsing signal, RF pulsingsignal, or otherwise). Frequency chirping is described in greater detailin connection with the RF pulsing signal in FIG. 4 below.

In one or more embodiments, the gas is pulsed such that during the gaspulsing on phase, reactant gas(es) and inert gas(es) (such as Argon,Helium, Xenon, Krypton, Neon, etc.) are as specified by the recipe.During the gas pulsing off phase, at least some of both the reactantgas(es) and inert gas(es) may be removed. In other embodiments, at leastsome of the reactant gas(es) is removed and replaced by inert gas(es)during the gas pulsing off phase. In an advantageous, at least some ofthe reactant gas(es) is removed and replaced by inert gas(es) during thegas pulsing off phase to keep the chamber pressure substantially thesame.

In one or more embodiments, during the gas pulsing off phase, thepercentage of inert gas(es) to total gas(es) flowed into the chamber mayvary from about X % to about 100%, wherein X is the percentage of inertgas(es) to total gas flow that is employed during the gas pulsing onphase. In a more preferred embodiment, the percentage of inert gas(es)to total gas(es) flowed into the chamber may vary from about 1.1 X toabout 100%, wherein X is the percentage of inert gas(es) to total gasflow that is employed during the gas pulsing on phase. In a preferredembodiment, the percentage of inert gas(es) to total gas(es) flowed intothe chamber may vary from about 1.5 X to about 100%, wherein X is thepercentage of inert gas(es) to total gas flow that is employed duringthe gas pulsing on phase.

The gas pulsing rate is limited at the high end (upper frequency limit)by the residence time of the gas in the chamber. This residence timeconcept is one that is known to one skilled in the art and varies fromchamber design to chamber design. For example, residence time typicallyranges in the tens of milliseconds for a capacitively coupled chamber.In another example, residence time typically ranges in the tens ofmilliseconds to hundreds of milliseconds for an inductively coupledchamber.

In one or more embodiments, the gas pulsing period may range from 10milliseconds to 50 seconds, more preferably from 50 milliseconds toabout 10 seconds and preferably from about 500 milliseconds to about 5seconds.

The source RF pulsing period is lower than the gas pulsing period inaccordance with embodiments of the invention. The RF pulsing frequencyis limited at the upper end by the frequency of the RF signal (e.g.,13.56 MHz would establish the upper limit for the RF pulsing frequencyif the RF frequency is 13.56 MHz).

FIG. 4 shows, in accordance with one or more embodiments of theinvention, other possible combinations. In FIG. 4, another signal 406(such as bias RF or any other periodic parameter) may be pulsed alongwith gas pulsing signal 402 and source RF pulsing signal 404 (pulsed asshown with 430 and 432). The pulsing of signal 406 may be madesynchronous or asynchronous with any other signals in the system.

Alternatively or additionally, another signal 408 (such as DC bias ortemperature or pressure or any other non-periodic parameter) may bepulsed along with gas pulsing signal 402 and source RF pulsing signal404. The pulsing of signal 408 may be made synchronous or asynchronouswith any other signals in the system.

Alternatively or additionally, another signal 410 (such as RF source orRF bias or any other non-periodic parameter) may be chirped and pulsedalong with gas pulsing signal 402. For example, while signal 410 ispulsing, the frequency of signal 410 may vary depending on the phase ofsignal 410 or another signal (such as the gas pulsing signal) or inresponse to a control signal from the tool control computer. In theexample of FIG. 1, reference 422 points to a region of higher frequencythan the frequency associated with reference number 420. An example of alower frequency 422 may be 27 MHz and a higher frequency 420 may be 60MHz. The pulsing and/or chirping of signal 410 may be made synchronousor asynchronous with any other signals in the system.

FIG. 5 shows, in accordance with an embodiment of the invention, thesteps for performing combination pulsing. The steps of FIG. 5 may beexecuted via software under control of one or more computers, forexample. The software may be stored in a computer readable medium,including a non-transitory computer readable medium in one or moreembodiments.

In step 502, a substrate is provided in a plasma processing chamber. Instep 504, the substrate is processed while pulsing both the RF sourceand the input gas. Optional pulsing of one or more other signals (suchas RF bias or another signal) is shown in step 506. In step 508, thefrequency, duty cycle, gas percentages, etc. may optionally be variedwhile pulsing the RF source and the input gas.

In one or more embodiments, the gas is pulsed such that there are atleast two phases per cycle, with cycles repeating periodically. Theother parameters, including the RF source signal, may be left unpulsed.During the first phase, the reactant gas (which may comprise multipledifferent etching and/or polymer-forming gases) to inert gas (such asone or more of Argon, Helium, Xenon, Krypton, Neon, etc.) ratio is at afirst ratio. During the second phase, the reactant gas to inert gasratio is at a second ratio different from the first ratio. If the ratioof reactant gas flow to total gas flow into the chamber is reduced(i.e., the ratio of inert gas to total gas flow into the chamber isincreased) during the second phase, the chamber contains a higherpercentage of the inert gas during the second phase than in the firstphase. In this case, an ion-dominant plasma results wherein the plasmaion flux is formed primarily with inert gas to perform the etching.

This is unlike the prior art situation where reactant gas is added topulse the gas. By increasing the percentage of the inert gas in thechamber without increasing the reactant gas flow into the chamber,embodiments of the invention achieve an ion-rich plasma to improve etchuniformity, directionality and/or selectivity.

In an embodiment, the ratio is changed not by adding any reactant (suchas etchant or polymer-forming) gases into the chamber but by reducingthe reactant gases flow rate such that the flow percentage of inert gasto reactant gas increases. In this embodiment, the chamber pressurewould inherently reduce during the second phase.

Alternatively or additionally, the ratio of reactant gas(es) to inertgas(es) may be changed by increasing the inert gas(es) flow into thechamber while keeping the reactant gas(es) flow into the chamber eitherconstant or by reducing the reactant gas(es) flow (but not by increasingthe reactant gases flow into the chamber). In an embodiment, the flow ofinert gas is increased to offset the reduction in the flow of reactantgas. In this embodiment, the chamber pressure remains substantially thesame during the first and second phases. In another embodiment, the flowof inert gas is increased but is insufficient to fully offset thereduction in the flow of reactant gas. In this embodiment, the chamberpressure is reduced during the second phase. In another embodiment, theflow of inert gas is increased more than sufficient to offset thereduction in the flow of reactant gas. In this embodiment, the chamberpressure is increased during the second phase.

As mentioned, in one or more embodiments, during the gas pulsing secondphase, the percentage of inert gas(es) to total gas(es) flowed into thechamber may vary from about X % to about 100%, wherein X is thepercentage of inert gas(es) to total gas flow that is present when theplasma chamber is stabilized for processing or the percentage of inertgas(es) to total gas flow that is present during the first phase. In amore preferred embodiment, the percentage of inert gas(es) to totalgas(es) flowed into the chamber may vary from about 1.1 X to about 100%.In a preferred embodiment, the percentage of inert gas(es) to totalgas(es) flowed into the chamber may vary from about 1.5 X to about 100%during the second phase.

The gas pulsing rate is limited at the high end (upper frequency limit)by the residence time of the gas in the chamber. As mentioned, forexample, residence time typically ranges in the tens of milliseconds fora capacitively coupled chamber. In another example, residence timetypically ranges in the tens of milliseconds to hundreds of millisecondsfor an inductively coupled chamber. Also as mentioned, in one or moreembodiments, the gas pulsing period may range from 10 milliseconds to 50seconds, more preferably from 50 milliseconds to about 10 seconds andpreferably from about 500 milliseconds to about 5 seconds.

In one or more embodiments, the inert gas added during the second phaseof the periodic pulsing may be the same inert gas or a different inertgas with different chemical composition and/or different constituentgases. Alternatively or additionally, the duty cycle of the gas pulsingrate may vary from 1% to 99%. Alternatively or additionally, the gaspulsing rate may be chirped, i.e., may change, during processing. Forexample, the gas pulsing may be done with a 5-second gas pulsing periodwith a 40% duty cycle and then switched to a 9-second gas pulsing periodwith either the same 40% duty cycle or a different duty cycle. Thechirping may be done periodically in accordance with a chirpingfrequency (such as 20 second chirping frequency wherein the gas pulsingfrequency may be changed every 20 seconds).

FIG. 6 shows, in accordance with one or more embodiments of theinvention, the steps for performing gas pulsing. The steps of FIG. 6 maybe executed via software under control of one or more computers, forexample. The software may be stored in a computer readable medium,including a non-transitory computer readable medium in one or moreembodiments.

In step 602, a substrate is provided in a plasma processing chamber. Instep 604, a plasma is generated in the chamber and stabilized with abaseline ratio of inert gas flow to reactant gas flow. In step 606, theratio of inert gas flow to reactant gas flow is increased in one phaseof the gas pulsing without increasing the reactant gas flow into thechamber. In step 608, the ratio of inert gas flow to reactant gas flowis decreased, relative to the ratio of inert gas flow to reactant gasflow of step 606, in another phase of the gas pulsing without increasingthe reactant gas flow into the chamber. In various embodiments, theratio of inert gas flow to reactant gas flow in step 608 may be thesubstantially the same as the ratio of inert gas flow to reactant gasflow of step 604 (stabilize plasma step) or may be higher or lower thanthe ratio of inert gas flow to reactant gas flow of stabilize step 604.In step 610, the substrate is processed while the gas is pulsed byhaving the aforementioned inert-to-reactant flow ratio fluctuatesperiodically with the ratios of steps 606 and 608.

FIGS. 7A and 7B illustrate, in accordance with embodiments of theinvention, different example variations of the gas pulsing schemediscussed in connection with FIG. 6. In the example of FIG. 7A, cases A,C, D, and E represents the various ratio of inert gas to reactant gas.In case A, the ratio of inert gas (I) to reactant gas (R) is 3:7, forexample. In case B, the ratio of inert gas to reactant gas is 8:1, forexample. In case C, the ratio of inert gas to reactant gas is 1:9, forexample. In case D, the gas flow into the chamber is essentially allinert. While example ratio values are given, the exact values of theratios are only illustrative; the important point is that these casesall have different ratios relative to one another.

In FIG. 7B, an example pulsing 702 may be ADAD in a preferred embodimentwhere the gas pulse may fluctuate periodically between case A and case Dof FIG. 7A and repeat.

Another example pulsing 704 may be ABABAB/ADAD/ABABAB/ADAD where the gaspulse may fluctuate periodically between case A and case B of FIG. 7A,then between cases A and D of FIG. 7A, and then back to cases A and B ofFIG. 7A and repeat.

Another example pulsing 706 may be ABABAB/ACAC/ABABAB/ACAC where the gaspulse may fluctuate periodically between case A and case B of FIG. 7A,then between cases A and D of FIG. 7A, and then back to cases A and B ofFIG. 7A and repeat.

Another example pulsing 708 may be ABABAB/CDCD/ABABAB/CDCD where the gaspulse may fluctuate periodically between case A and case B of FIG. 7A,then between cases C and D of FIG. 7A, and then back to cases A and B ofFIG. 7A and repeat.

Another example pulsing 710 may be ABABAB/CDCD/ADAD/ABABAB/CDCD/ADADwhere the gas pulse may fluctuate periodically between case A and case Bof FIG. 7A, then between cases C and D of FIG. 7A, then between cases Aand D of FIG. 7A and then back to cases A and B of FIG. 7A and repeat.

Other examples may include 4 phases such as ABAB/CDCD/ADAD/ACAC andrepeat. The complex pulsing is highly advantageous for processesinvolving, for example, in situ etch-then-clean or multi-step etches,etc.

In another embodiment, the gas pulsing of FIGS. 6, 7A and 7B may becombined with asynchronous or synchronous pulsing of the RF bias signalthat is supplied to the powered electrode. In an example, when the gasis pulsed to a high inert gas percentage or 100% or near 100% inert gaspercentage in one phase of the gas pulsing cycle, the RF bias signal ispulsed high. When the gas is pulsed to a lower inert gas percentage inanother phase of the gas pulsing cycle, the RF bias signal is pulsed lowor zero. In various embodiments, the pulsing frequency of the RF biassignal may be the same or different compared to the pulsing frequency ofthe gas pulsing. In various embodiments, the duty cycle of the RF biassignal may be the same or different compared to the duty cycle of thegas pulsing. Chirping may be employed with one or both of the RF biassignal pulsing and the gas pulsing if desired.

In each of the gas pulsing examples, the pulsing frequency, the numberof pulses, the duty cycle, etc., may be varied kept constant throughoutthe etch or may vary periodically or non-periodically as required.

As can be appreciated from the foregoing, embodiments of the inventionprovide another control knob that can widen the process window for etchprocesses. Since many current plasma chambers are already provided withpulsing valves or pulsing mass flow controllers, the implementation ofgas-pulsing in accordance with FIGS. 6-7A/7B and the discussion hereinmay be achieved without requiring expensive hardware retrofitting.Further, if RF pulsing is desired in conjunction with gas pulsing, manycurrent plasma chambers are already provided with pulse-capable RF powersupplies. Accordingly, the achievement of a wider process window viagas/RF power pulsing may be obtained without requiring expensivehardware retrofitting. Current tool owners may leverage on existing etchprocessing systems to achieve improved etches with minor softwareupgrade and/or minor hardware changes. Further, by having improvedand/or more granular control of the ion-to-radical flux ratios,selectivity and uniformity and reverse RIE lag effects may be improved.For example, by increasing the ion flux relative to radical flux mayimprove the selectivity of one layer to another layer on the substratein some cases. With such improved control of ion-to-radical, atomiclayer etch (ALE) may be more efficiently achieved.

In one or more embodiments, mixed mode pulsing (MMP) etching isdisclosed whereby the etching involves repeating a multi-step sequence,each sequence involving at least an MMP preparation (MMPP) phase and anMMP reactive (MMPR) phase. The mixed mode pulsing is configured to morefully separate ions and neutral radicals temporally (i.e., in time) insitu in a production inductively coupled plasma (ICP, also known as TCPor transformer coupled plasma in some instances) chamber or in acapacitively coupled plasma (CCP) chamber.

To clarify, the MMP etching is practiced in a production inductivelycoupled plasma (ICP) chamber to accomplish, for example, atomic layeretching (ALE) or very precise etching of the type that typicallyrequires the use of another chamber (such as a beam-type chamber) in theprior art. The fact that the inventive MMP etching allows such atomiclayer etching (ALE) or precise layer-by-layer etching in the productionICP chamber substantially improves the overall throughput since there isno need to transfer the substrate from the production chamber intoanother chamber for such ALE or precise layer-by-layer etching. Theinventive MMP etching also eliminates the need for specialized ALE orlayer-by-layer etching equipment, thereby reducing manufacturing cost.MMP etching is also employed in a production ICP chamber to accomplishhigh selectivity etching, as will be discussed later herein.

To clarify, an ICP chamber, which construction is well known, involvesthe use of at least one RF-powered inductive coil for inductivelycoupling, through a dielectric window, RF energy to a plasma cloudformed from reactant and other gases. The plasma cloud is disposed belowthe dielectric window but above a substrate for etching the substrate.The substrate itself is disposed on a work piece holder, typically anESC chuck for example. The work piece holder may also be supplied withits own RF signal(s), if desired. RF energy provided to the work pieceholder is known as bias power. ICP chambers are commonly employed forproducing substrates in today's IC (integrated circuit) fabricationfacilities and are suitable for high throughput.

In one or more embodiments, the MMP preparation phase involves usingplasma to generate radicals (also known as neutrals) from reactantgases. No bias power is applied to the substrate work piece holder inone embodiment. The elimination or minimal usage of bias power iscritical for reducing the influence of ions during the MMP preparationphase.

Using silicon etching as an example, the reactant gas may be chlorine(Cl₂), for example. Depending on the material to be etched, otherreactant gases may be for example C_(x)F_(y) or CH_(x)F_(y) (where x andy are integers), CH₃Cl, N₂, BCL₃, O₂, or other commonly used reactantgases for etching substrates. During the MMP preparation phase, a plasmais formed from the reactant gas and allowed to adsorb into exposed toplayer of the silicon substrate. The MMP preparation phase is timed toallow the adsorption to penetrate at least one atomic layer of siliconin one embodiment and multiple atomic layers of silicon in anotherembodiment if a more aggressive etch is desired.

Parameters of the chambers are optimized to increase the speed ofadsorption without unduly removing the adsorbed SiCl layer in the MMPpreparation phase. For example, the inductive coil RF frequency may bedifferent during the MMP preparation phase relative to the MMP reactivephase to promote adsorption in one or more embodiments. Alternatively oradditionally, as another example, the substrate or the substrate surfacemay be heated (or cooled) during the MMP preparation phase.Alternatively or additionally, as another example, the inductive coil RFpower may be pulsed on and off (either symmetrically ornon-symmetrically with respect to the duration of the on and off cycles)to reduce ion energy and/or to promote adsorption. In one or moreembodiments, inductive coil RF signal(s) may be chirped with differentRF frequencies during a single MMP preparation phase.

Alternatively or additionally, as another example, the chamber gapbetween the electrodes (of a variable gap chamber) may be set largerduring the MMP preparation phase relative to the MMP reactive phase inorder to lower the ion energy level, reduce self-bias, and/or reduce theinfluence of ions. Alternatively or additionally, as another example, ifions are incidentally generated, the parameters may be adjusted so thatthe ion energy is below the level required to etch the adsorbed SiCllayer in one or more embodiments. For example, chamber pressure may bekept high (e.g., above 40 mT in one example etch) during the MMPpreparation phase to reduce the ion energy in one or more embodiments.

In one or more embodiments, some non-reactive gas (such as argon) may beallowed during the MMP preparation phase. However, such non-reactive gasflow during the MMP preparation phase, if allowed, is set to be lowerthan the amount of non-reactive gas flow that occurs during the MMPreactive phase. The same non-reactive gas may be employed in both theMMP preparation phase and the MMP reactive phase or differentnon-reactive gases may be employed. In other embodiments, the MMPpreparation phase involves only reactive gases (such as chlorine) and nonon-reactive gases (such as argon) is employed during the MMPpreparation phase.

In one or more embodiments, different reactive gases may be employedsimultaneously during a single MMP preparation phase. Alternatively, inone or more embodiments, different reactive gases may be flowed insequential order into the chamber during the MMP preparation phase. Thismay be advantageous for etching binary or other compounds. If desired,the chamber may be flushed with a non-reactive gas (such as argon) inbetween the flowing of different reactive gases during the MMPpreparation phase.

For ALE etches where a single atomic layer etching is desired or whereetching of a small number of atomic layers is desired, it is preferablethat no bias power is applied during the MMP preparation phase. Inapplications where a higher throughput is desired while maintainingprecision, a small amount of bias power (relative to the bias powerapplied during the MMP reactive phase) may be applied during the MMPpreparation phase to promote some implantation of the reactive species.If the small amount of bias power is applied during the MMP preparationphase, this bias power may be kept constant during the MMP preparationphase or may be pulsed (either asynchronously or synchronously with theinductive coil RF pulsing) if desired.

After the MMP preparation phase, there is an MMP reactive phase duringwhich reactant gases are not permitted to be present in the chamber anda plasma is generated from non-reactive gases (such as inert gases) toform a plasma having a specific ion energy window. In theabove-mentioned silicon example, argon may be employed as thenon-reactive gas during the MMP reactive phase. Alternatively oradditionally, the non-reactive gas(es) may be Xe, He, Ne or clusters ofany of the above.

In the MMP reactive phase, the ion energy of the Ar+ ions (which isgenerated from non-reactive gases in the absence of reactant gases) isabove the threshold required to etch the adsorbed SiCl layer but desiredto be below the threshold required to etch the non-adsorbed Si substratebelow. For example, the ion energy window may be between 50 eV and 70 eVfor etching silicon in one embodiment. This is one aspect of theself-limiting feature of one embodiment of the MMP etching that permitsprecise control of the etching and causes the etching to stop when theadsorbed layer is all etched away. Another aspect of the self-limitingfeature of one embodiment of the MMP etching is control of the depth ofthe adsorbed SiCl layer during the MMP preparation phase, in one or moreembodiments. Another aspect of the self-limiting feature of oneembodiment of the MMP etching is the length of time of the MMP reactivephase to ensure that only some or all of the adsorbed SiCl layer isremoved and the underlying Si material is not etched. Another aspect ofthe self-limiting feature of one embodiment of the MMP etching is thelength of time of the MMP preparation phase.

Of significant note is the fact that the bias power is turned on duringthe MMP reactive phase (in contrast, the bias power is preferablycompletely off during the MMP preparation phase or is turned on to alevel lower than the bias power level in the MMP reactive phase to helpensure that the ion energy remains below the threshold for ion-inducedetching of the adsorbed layer). Other parameters of the chamber may beoptimized to promote the directional etching of the adsorbed SiCl layerby the plasma that is formed from the non-reactive gas. For example, thechamber pressure may be reduced in the MMP reactive phase (relative tothe higher chamber pressure of the MMP preparation phase) in order toreduce the number of collisions, thereby reducing the angle distributionof the ions and resulting in a more directional etch. As anotherexample, the bias power may be pulsed on and off multiple times during asingle MMP reactive phase. Alternatively or additionally, as anotherexample, the RF inductive coil power may be pulsed on and off multipletimes during a single MMP reactive phase.

Alternatively or additionally, as another example, both the bias powerand the RF inductive coil power may be pulsed multiple times, eithersynchronously or asynchronously relative to one another, during a singleMMP reactive phase. Alternatively or additionally, as another example,the inductive coil RF frequency may be different (such as higher toincrease the ion energy distribution function) during the MMP reactivephase relative to the MMP preparation phase. In an example, the MMPreactive phase may employ 60 MHz for inductive coil RF signal while theMMP preparation phase may employ 13.56 MHz for the inductive coil RFsignal during the MMP reactive phase. Alternatively or additionally, asanother example, the bias RF and/or the inductive coil RF may be chirpedwith different RF frequencies during a single MMP reactive phase.Alternatively or additionally, a tailored bias waveform may be employedduring the MMP reactive phase to reduce the ion energy. To elaborate, atailored bias waveform is an RF bias signal having a waveform tailoredor shaped (e.g., clipped or modified) in order to optimize or regulatethe ion energy).

The MMP preparation phase and the following MMP reactive phase form acycle, which cycle may be repeated a number of times until etching isdeemed completed. To ensure complete or substantially complete removalof the reactant gas from the chamber prior to the MMP reactive phase, anMMP transition phase may (but not required in all cases) be interposedin between the MMP preparation phase and the MMP reactive phase to, forexample, facilitate more complete removal of the reactant gas(es) and/orto stabilize and/or prepare the chamber for the MMP reactive phase.Alternatively or additionally, another transition phase may be employedin between the MMP transition phase of a preceding cycle and an MMPpreparation phase to stabilize and/or prepare the chamber for the MMPpreparation phase, in one or more embodiments.

Because of the need to perform the MMP reactive phase without usingreactant gases (or as little reactant gas as possible compared to theMMP preparation phase), a limit is imposed on how fast the etch can bepulsed between the MMP preparation phase and the MMP transition phase.Since it takes some finite amount of time to evacuate a gas from achamber, the transition between the MMP preparation phase and the MMPreactive phase is limited, in one embodiment, by the gas residence timeof the chamber, which can be readily calculated by one skilled in theart. As mentioned, an MMP transition phase may be employed (but notrequired in all cases) in between the MMP preparation phase and the MMPreactive phase to help prepare the chamber for the MMP reactive phase(such as to ensure that all reactive gases are removed or to stabilizethe chamber in one embodiment).

In one or more embodiments, the MMP preparation phase may be betweenabout 0.01 second to about 5 seconds, more preferably from 0.2 second toabout 1 second. In one or more embodiments, the MMP reactive phase maybe between about 0.01 second to about 5 seconds, more preferably from0.05 second to about 1 second. In one or more embodiments, the switchingrate may be around 1 Hz. This is a differentiation from techniques thatinvolve synchronous or asynchronous pulsing of the TCP and/or TCP/biaspower that does not take gas residence time into consideration and/ordoes not involve the removal of reactant gases from the chamber duringthe MMP reactive phase.

Note that the use of a grid or some other structures to accelerate theions toward the substrate is not necessary, in one or more embodiments.Also note that the MMP preparation and etching phases are advantageouslyperformed completely in situ in the same ICP chamber that is employedfor other substrate processing steps.

In one or more embodiments, the MMP reactive phase may be timed or maybe terminated responsive to chamber monitoring (using for exampleoptical emission spectroscopy techniques). In one or more embodiments,the reactive etching during the MMP reactive phase is allowed to etchonly a single atomic layer (ALE). In this example, the adsorption may becontrolled such that the adsorbed layer is around one atomic layerthick. In one or more embodiments, the reactive etching during the MMPreactive phase is allowed to proceed to etch thorough multiple atomiclayers of the adsorbed substrate surface. In one or more embodiments,parameters of the chamber may be adjusted such that there is a bulk MMPreactive etch, followed by a more precise but slower monolayer MMPreactive etch during a single MMP reactive phase.

In one or more embodiments, MMP etching is employed to improveselectivity. Up to now, the MMP etching example involves a singlematerial (such as silicon in the example). As mentioned above, theselection of the reactant gas during the MMP preparation phase involvesselecting a suitable reactant gas for etching silicon (such as Cl₂), andthe configuring of the ion energy level during the MMP reactive phaseinvolves selecting an ion energy level suitable for etching the adsorbedSiCl layer but not the bulk non-adsorbed Si material below.

To improve selectivity between two materials when etching a substrate,the reactant gas may be chosen (for use during the MMP preparationphase) such that the reactant gas forms a plasma that favors adsorptioninto one material over the other material. Additionally oralternatively, the gas chosen may be adsorbed onto both materials butfavors the formation of volatile compounds on one material over theother material. Additionally or alternatively, the gas chosen may causedeposition more on one material than on another material. Additionallyor alternatively, the gas chosen may decrease the bonding strength atthe surface of one material to a greater extent than the decrease inbonding strength at the surface of another material. Additionally oralternatively, the ion energy during the MMP reactive phase may bechosen to more aggressively etch one material over another material. Anexample of this MMP selectivity etching is etching polysilicon but notoxide. In this case, the reactant gas may be chosen to be Cl₂ during theMMP preparation phase, which does not tend to etch oxide based onchemistry considerations alone, and the ion energy threshold during theMMP reactive phase may be 70 eV for polysilicon and 80 eV for oxide, forexample.

FIG. 8 shows, in accordance with an embodiment of the invention,conceptual MMP etching cycles (showing species density versus time) forthe silicon etching example, with each cycle involving at least an MMPpreparation phase and an MMP reactive phase. With reference to FIG. 8,an MMP etching cycle 802 involves at least an MMP preparation phase 804and an MMP reactive phase 806. Chamber and gas conditions for each ofMMP preparation phase 804 and MMP reactive phase 806 are discussedabove. Of significant note is the fact that radicals and ions areseparated in time, with a high amount of radicals and substantially noions during the MMP preparation phase 804 and high amount of ions andsubstantially no radicals during the MMP reactive phase 806.

FIG. 9 shows, in accordance with an embodiment of the invention, otherconceptual MMP etching cycles where some ions exist in the MMPpreparation phase 904. Ions may be present as an unintended side-effectof plasma generation but is kept below (by manipulating chamberparameters) the threshold ion energy level necessary to etch theadsorbed SiCl surface during the MMP preparation phase 904. Ions mayalso be intentionally introduced by employing some small amount of biaspower to promote implantation as discussed earlier. Nevertheless, theion energy is kept below the threshold ion energy level necessary toetch the adsorbed surface during the MMP preparation phase.

During the MMP reactive phase 906, reactant gas is excluded from thechamber and preferably substantially no reactants are present in thechamber during the MMP reactive phase 906. Chamber and gas conditionsfor each of MMP preparation phase 904 and MMP reactive phase 906 arediscussed above. As mentioned earlier, an MMP transition phase may beinterposed between MMP preparation phase 904 and MMP reactive phase 906if desired. Alternatively or additionally, another MMP transition phasemay be interposed between preceding MMP reactive phase 906 and the MMPpreparation phase 908 of the next MMP cycle.

FIG. 10 shows, in accordance with an embodiment of the invention, amethod for performing MMP etching in a production ICP chamber. In step1000, a substrate is provided in the production ICP chamber to preparefor the in situ MMP etch. It should be understood that the substrate mayhave been disposed in the chamber for some time and other processingsteps (such as bulk etch) may have already taken place prior to the MMPetching. In step 1002, the chamber is configured to operate in the MMPpreparation phase. In this MMP preparation phase, reactant gas isallowed to adsorbed into the substrate surface with the assistance ofplasma. The depth of adsorption is controlled to form one aspect of theself-limiting etch (to be performed during a subsequent MMP reactivephase). Other alternative or additional chamber conditions for the MMPpreparation phase are discussed above.

In step 1004, the chamber is configured to etch the substrate in the MMPreactive phase. In this MMP reactive phase, reactant gas is excludedfrom the chamber and the bias power is increased (or turned on) topromote plasma-assisted removal of the adsorbed layer(s) using a plasmaformed from inert gas(s). The ion energy during the MMP reactive phaseis set to be higher than the level necessary to etch the adsorbed layerbut lower than the level necessary to etch the non-adsorbed layerunderneath, thereby essentially self-limit the etch. Other alternativeor additional chamber conditions for the MMP reactive phase is discussedabove. The MMP cycle including at least the MMP preparation phase andthe MMP reactive phase is repeated (1012) until the MMP etch is deemed(1006) completed (1008).

As can be appreciated from the foregoing, embodiments of the MMP etchare highly suitable for ALE etch or precise etches (such as etches forfabrication 3-D logic or memory devices or MRAM) or high selectivityetches. Furthermore, embodiments of the invention reduce substratedamage and result in a flat etch front. The self-limiting nature and/orhigh selectivity of the MMP etch helps reduce structural damage tolayer(s) or structure(s) that should not be etched. In some cases, theself-limiting nature of the MMP etch helps improve etch precision and/oretch profile and/or may reduce the need for overetching.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents, whichfall within the scope of this invention. For example, although the MMPetch has been disclosed using an ICP chamber example, MMP etching may beperformed in a capacitively coupled plasma (CCP) chamber if desired.With respect to the MMP etch, when the etch is performed in acapacitively coupled plasma chamber, the supplied higher RF frequencymay be considered the source RF and the supplied lower RF frequency maybe considered the bias RF irrespective whether these RF signals areprovided to only one plate of the chamber or split up among the platesof the chamber.

As another example, the pulsing techniques discussed in the figures maybe combined in any combination to suit the requirement of a particularprocess. For example, the duty cycle variance may be practiced withtechniques discussed with any one (or part of any one or a combinationof multiple ones) of the figures. Likewise, the frequency chirping maybe practiced with techniques discussed with any one (or part of any oneor a combination of multiple ones) of the figures and/or with duty cyclevariance. Likewise, inert gas substitution may be practiced withtechniques discussed with any one (or part of any one or a combinationof multiple ones) of the figures and/or with duty cycle variance and/orwith frequency chirping. The point is although techniques are discussedindividually and/or in connection with a specific figure, the varioustechniques can be combined in any combination in order to perform aparticular process.

Although various examples are provided herein, it is intended that theseexamples be illustrative and not limiting with respect to the invention.Also, the title and summary are provided herein for convenience andshould not be used to construe the scope of the claims herein. If theterm “set” is employed herein, such term is intended to have itscommonly understood mathematical meaning to cover zero, one, or morethan one member. It should also be noted that there are many alternativeways of implementing the methods and apparatuses of the presentinvention.

What is claimed is:
 1. A plasma processing system for processing asubstrate using mixed-mode pulsing, the plasma processing systemcomprising: a substrate; a plasma processing chamber for processing thesubstrate; a work piece holder within an interior region of the plasmaprocessing chamber; at least one plasma generating source; at least onereactive gas source for providing at least a first reactive gas into theinterior region of the plasma processing chamber; at least onenon-reactive gas source for providing at least a first non-reactive gasinto the interior region of the plasma processing chamber; and atangible computer-readable medium storing computer-readable instructionsfor: (a) disposing the substrate on the work piece holder within theinterior region; (b) performing a mixed-mode pulsing (MMP) preparationphase, including flowing the first reactive gas into the interiorregion, exciting the first reactive gas with a first RF signal having afirst RF frequency, the first RF signal representing an RF signal havingchirped frequencies, and forming a first plasma with at least the firstreactive gas to process the substrate with the first plasma; (c)performing a mixed mode pulsing (MMP) reactive phase, including flowingat least the first non-reactive gas into the interior region, andforming a second plasma with at least the first non-reactive gas toprocess the substrate with the second plasma, wherein the second plasmais formed with a flow of the first reactive gas during the MMP reactivephase that is less than a flow of the first reactive gas during the MMPpreparation phase; and (d) repeating steps (b) and (c) for a pluralityof times.
 2. The system of claim 1 further comprising computer-readableinstructions for providing that no first reactive gas is flowed into theinterior region during the MMP reactive phase.
 3. The system of claim 1wherein the plasma processing chamber comprises an inductively coupledplasma processing chamber.
 4. The system of claim 1 wherein the plasmaprocessing chamber comprises a capacitively coupled plasma processingchamber.
 5. The system of claim 1 wherein the at least one non-reactivegas source further provides a second non-reactive gas, and wherein thetangible computer-readable medium further comprises storingcomputer-readable instructions for providing that the secondnon-reactive gas is flowed into the interior region during the MMPpreparation phase.
 6. The system of claim 1 further comprisingcomputer-readable instructions for providing that the first non-reactivegas is also flowed into the interior region during the MMP preparationphase.
 7. The system of claim 1 further comprising computer-readableinstructions for providing that no bias power is applied to the workpiece holder during the MMP preparation phase.
 8. The system of claim 7further comprising computer-readable instructions for providing thatbias power having a bias power level greater than zero is applied to thework piece holder during the MMP reactive phase.
 9. The system of claim1 further comprising computer-readable instructions for flowing a secondreactive gas different from the first reactive gas into the interiorregion during the MMP reactive phase.
 10. The system of claim 9 furthercomprising computer-readable instructions for providing that no firstreactive gas is flowed during the MMP reactive phase.
 11. The system ofclaim 1 further comprising computer-readable instructions for providingthat a first bias power is applied to the work piece holder during theMMP preparation phase and a second bias power having a different powerlevel from a power level of the first bias power is applied to the workpiece holder during the MMP reactive phase.
 12. The system of claim 11further comprising computer-readable instructions for providing that thepower level of the second bias power is higher than the power level ofthe first bias power.
 13. The system of claim 1 further comprisingcomputer-readable instructions for providing that the plasma processingchamber is configured during the MMP reactive phase to generatenon-reactive ions having a level of ion energy that is higher thanrequired to etch an adsorbed layer on a surface of the substrate butinsufficient to etch a non-adsorbed layer of the substrate, andproviding that the adsorbed layer formed during the MMP preparationphase.
 14. A plasma processing system for processing a substrate usingmixed-mode pulsing, the plasma processing system comprising: asubstrate; a plasma processing chamber for processing the substrate; awork piece holder within an interior region of the plasma processingchamber; at least one plasma generating source; at least one reactivegas source for providing at least a first reactive gas into the interiorregion of the plasma processing chamber; at least one non-reactive gassource for providing at least a first non-reactive gas into the interiorregion of the plasma processing chamber; and a tangiblecomputer-readable medium storing computer-readable instructions for: (a)disposing the substrate on a work piece holder within the interiorregion; (b) performing a mixed-mode pulsing (MMP) preparation phase,including flowing the first reactive gas into the interior region, andforming a first plasma with at least the first reactive gas to processthe substrate with the first plasma; (c) performing a mixed mode pulsing(MMP) reactive phase, including flowing at least the first non-reactivegas into the interior region, and forming a second plasma with at leastthe first non-reactive gas to process the substrate with the secondplasma, wherein the second plasma is formed with a flow of the firstreactive gas during the MMP reactive phase that is less than a flow ofthe first reactive gas during the MMP preparation phase, wherein theplasma processing chamber is configured during the MMP reactive phase togenerate non-reactive ions having a level of ion energy that is higherthan required to etch an adsorbed layer on a surface of the substratebut insufficient to etch a non-adsorbed layer of the substrate, theadsorbed layer formed during the MMP preparation phase; and (d)repeating steps (b) and (c) for a plurality of times.
 15. The system ofclaim 14 further comprising computer-readable instructions for providingthat no first reactive gas is flowed into the interior region during theMMP reactive phase.
 16. The system of claim 14 further comprisingcomputer-readable instructions for providing that no bias power isapplied to the work piece holder during the MMP preparation phase. 17.The system of claim 16 further comprising computer-readable instructionsfor providing that bias power having a bias power level greater thanzero is applied to the work piece holder during the MMP reactive phase.18. The system of claim 17 further comprising computer-readableinstructions for providing that the bias power is pulsed during the MMPreactive phase.
 19. The system of claim 14 further comprising at leastone inductive antenna, and further comprising computer-readableinstructions for providing that the at least one inductive antenna isexcited with a first RF signal having a first RF frequency during theMMP preparation phase, and the at least one inductive antenna is excitedwith a second RF signal having a second RF frequency that is differentfrom the first RF frequency during the MMP reactive phase.
 20. Thesystem of claim 14 further comprising at least one inductive antenna,and further comprising computer-readable instructions for providing thatthe at least one inductive antenna is excited with a first RF signalhaving a first RF frequency during the MMP preparation phase, the firstRF signal representing a pulsed RF signal.
 21. The system of claim 14further comprising at least one inductive antenna, and furthercomprising computer-readable instructions for providing that the atleast one inductive antenna is excited with a first RF signal having afirst RF frequency during the MMP reactive phase, the first RF signalrepresenting a pulsed RF signal.
 22. A plasma processing system forprocessing a substrate using mixed-mode pulsing, the plasma processingsystem comprising: a substrate; a plasma processing chamber forprocessing the substrate; a work piece holder within an interior regionof the plasma processing chamber; at least one reactive gas source forproviding at least a first reactive gas into the interior region of theplasma processing chamber; at least one non-reactive gas source forproviding at least a first non-reactive gas into the interior region ofthe plasma processing chamber; at least one gas pulsing valve forflowing a first reactive gas into the interior region during amixed-mode pulsing (MMP) preparation phase; at least one gas pulsingvalve for flowing a first non-reactive gas into the interior regionduring a mixed-mode pulsing (MMP) reactive phase; and, at least oneplasma generating source comprising a pulse-capable RF power supply;and, a tangible computer-readable medium storing computer-readableinstructions for: (a) flowing the first reactive gas during the MMPreactive phase at a flow rate that is less than the flow rate of thefirst reactive gas during the MMP preparation phase; and, (b) forsupplying an RF signal having chirped frequencies to excite the firstreactive gas during the MMP preparation phase.
 23. The system of claim22 wherein the system further comprises a computer for controlling theplasma processing chamber to flow no first reactive gas into theinterior region during the MMP reactive phase.
 24. The system of claim22 wherein the plasma processing chamber comprises an inductivelycoupled plasma processing chamber.
 25. The system of claim 22 whereinthe plasma processing chamber comprises a capacitively coupled plasmaprocessing chamber.
 26. The system of claim 22 wherein the at least onenon-reactive gas source further provides a second non-reactive gas, andwherein the second non-reactive gas is flowed into the interior regionduring the MMP preparation phase.
 27. The system of claim 22 wherein thesystem further comprises a computer for controlling the plasmaprocessing chamber to also flow the first non-reactive gas into theinterior region during the MMP preparation phase.
 28. The system ofclaim 22 wherein the system further comprises a computer for controllingthe plasma processing chamber to apply no bias power to the work pieceholder during the MMP preparation phase.
 29. The system of claim 28wherein bias power having a bias power level greater than zero isapplied to the work piece holder during the MMP reactive phase.
 30. Thesystem of claim 22 wherein a second reactive gas different from thefirst reactive gas is flowed into the interior region during the MMPreactive phase.
 31. The system of claim 30 further comprising a computerfor controlling the plasma processing chamber to flow no first reactivegas during the MMP reactive phase.
 32. The system of claim 22 wherein afirst bias power is applied to the work piece holder during the MMPpreparation phase and a second bias power having a different power levelfrom a power level of the first bias power is applied to the work pieceholder during the MMP reactive phase.
 33. The system of claim 32 furthercomprising wherein the power level of the second bias power is higherthan the power level of the first bias power.
 34. The system of claim 22wherein the system further comprises a computer for controlling theplasma processing chamber to generate during the MMP reactive phasenon-reactive ions having a level of ion energy that is higher thanrequired to etch an adsorbed layer on a surface of the substrate butinsufficient to etch non-adsorbed layer of the substrate, and providingthat the adsorbed layer is formed during the MMP preparation phase.